COURSE 4 PROJECTS - YEAR 2012/13

HAS ROOM TEMPERATURE SUPERCONDUCTIVITY BEEN OBSERVED IN WATER-TREATED GRAPHITE POWDER?

Supervisor: Dr. Elizabeth Blackburn
Students: Peter Diwell and Matthew Robson

Summary and Perspectives (by PD and MR)

Following a report of a magnetic hysteresis loop in water-treated graphite powder at room temperature suggestive of superconductivity (Scheike et al., Advanced Materials 24, 5826 (2012)), we have performed magnetisation measurements on graphite powder and highly oriented graphite powder to try to reproduce these results. No superconductor-like hysteresis has been observed. A ferromagnetic hysteresis loop is obtained in measurements on all the graphite samples and in measurements made in the absence of a sample. Although we measure a low-field hysteresis in both the untreated and the treated graphite powder that is ferromagnetic, we show that subtracting the the diamagnetic background from the data incorrectly produces a hysteresis loop which closely resembles that reported as indicative of superconductivity, although here the signal is produced by ferromagnetic impurities.

This work is referenced in a Commentary on an article in Papers of Physics, and is critiqued in a Reply to this Commentary.

COURSE 4 PROJECTS - YEAR 2011/12

QUANTUM FLUCTUATIONS IN SUPERCONDUCTING NIOBIUM

Supervisor: Dr. Elizabeth Blackburn
Student: Robin Edge

Summary and Perspectives

Rob engaged in a study of the heat capacity of niobium close to the superconducting transition in niobium, using a very sensitive heat capacity rig. The aim was to look for signs of the flux line lattice melting. The measurements showed no signs of this transition in the range studied. Rob developed some electronics to stabilize the measurements, and then collected data in several crystal orientations.

COURSE 4 PROJECTS - YEAR 2010/11

X-RAY STUDY OF THIN FILMS OF INDIUM TIN OXIDE, A TRANSPARENT CONDUCTOR

Supervisor: Dr. Elizabeth Blackburn
Student: Daniel Farnell

Summary and Perspectives (by DF)

Indium tin oxide (ITO) is one of the most widely used transparent conducting films because of its electrical conductivity and optical transparency, as well as the ease with which it can be deposited as a thin film. The aim of this project was to examine a series of ITO films that had been prepared under a range of different growth conditions, to study any structural changes brought about by the growth method. The primary goal was to establish the detailed structural properties of the films using x-ray diffraction from the (222) planes, and to compare those features with the conducting properties of each film.

COURSE 4 PROJECTS - YEAR 2009/10

POLYSTYRENE AND POLYANILINE THIN FILMS

Supervisor: Dr. Elizabeth Blackburn
Students: Amy Fitzgerald and Charlotte O'Neale

Summary and Perspectives (by AF and CO'N)

Polystyrene films made from polystyrene-toluene solutions and created by spin-coating were investigated. The effect of the parameters of spin speed and solution concentration was found to be in general agreement with the literature. Polyaniline, a conducting polymer, was successfully dissolved in N-methylpyrrolidone (NMP) by dissolving emeraldine base in NMP and then protonating with camphor-sulphonic acid. However, the spin casting parameters for this solution were not perfected. Mixed polyaniline-polystyrene films were obtained by blending a solution of polyaniline dissolved in NMP with a soution of polystyrene in toluene.

There are many improvements that could be made to the film growing process. These include:

1. Investigating spin coating parameters for polyaniline in NMP to create smooth films.

2. Investigating spin coating parameters for polymer blends to create smooth films.

COURSE 4 PROJECTS - YEAR 2007/8

ULTRA-HIGH PURITY SUPERCONDUCTORS AT LIQUID He TEMPERATURES

Supervisor: Professor Ted Forgan
Room: Physics East 203A
Tel: 44678
e-mail: E.M.Forgan@bham.ac.uk

Summary

In the Condensed Matter Group, we have an ongoing international programme of research into the behaviour of lines of quantised magnetic flux in superconductors [1]. The impact of this research was recognised by the award of the 2004 Mott Medal and Prize to Prof. Ted Forgan, supervisor of this project.

One of the interesting topics of this field is the observation and understanding of behaviour of flux lines in single crystals of ultra-high-purity superconductors. One of the difficulties is to measure exactly how pure our samples are. A suitable method is to measure the resistivity at low temperatures, where the scattering of the electrons is dominated by impurities. The project would consist of experimental work at liquid helium temperatures to measure the resistivity of a series of single crystal samples of a low-Tc superconductor - niobium, leading on to neutron diffraction and heat capacity experiments on these samples. The resistivity would be measured by a non-contact method, suitable for such high-quality samples. To suppress the superconductivity, the sample would be measured in a field provided by a small superconducting coil, which would be designed and made by the project students.

Background

We have been preparing extremely pure single crystals of the superconducting element niobium in order to observe the flux lines by neutron scattering [2,3] and heat capacity measurements. Such pure crystals are extremely uniform and allow us to search for the long-predicted but not-observed effect of flux line melting in a low-Tc superconductor. To get a measure of the purity we wish to measure the resistivity of the samples at low temperatures. There are problems with this: The sample goes superconducting at low temperatures - so its resistivity is zero for all impurity levels! One way round this, which we use at present, is to warm it above the Tc of 9.27 K. However, in pure samples, scattering of electrons by lattice vibrations is already noticeable at this temperature, so one has to extrapolate a great deal to obtain the zero-temperature resistivity.

An alternative solution is to apply a magnetic field above the critical field for destruction of superconductivity. This requires about 0.5 T for niobium, and a small superconducting coil can fairly easily supply this. We propose the design and production of this as part of the project.

Another consideration is how to measure the resistivity of a cm-sized sample when its resistance is about a nano-ohm! This can be done without attaching current leads by a 'non-contact' method invented many years ago [4]. Basically, one induces a large current in the sample by applying a rapidly changing magnetic field to it. Then, one uses a pick-up coil and digital memory oscilloscope to observe the decay of the induced eddy currents. The lower the resistivity of the sample, the slower is the longest time constant of the decay. This project should appeal to a pair of experimentalists with an adventurous bent and an interest in using cryogenic techniques and computer-based data acquisition.

Subject to beamtime allocations, students taking part in this project may have the chance to crown their project by taking part in neutron diffraction experiments at the world's highest flux reactor at the Institut Laue-Langevin in Grenoble. However, the major work of this project would be carried out in Birmingham.

COMPUTATIONS FOR SUPERCONDUCTORS AND MAGNETIC FIELDS

Supervisor: Dr Mark Colclough
Room: Physics East 204
Tel: 43948
e-mail: m.s.colclough@bham.ac.uk

Summary

This is a pair of closely-related computational superconductivity projects:

(i) is to perform computer calculations of the distribution of currents and magnetic fields in the vicinity of a superconductor. The results are necessary to interpret the results of experiments on superconducting devices - and could also be used to model superconducting levitation.

(ii) is the calculation of supercurrent distribution in Josephson junctions from experimental data. The Josephson junction is the active element of superconducting electronics. It is a controlled weakening in an otherwise strongly-superconducting current path. When such a junction has been made, it is important to know not only the magnitude of the weakening, but also its distribution across the current path. For example, is the path weakened more at the edges, at random spots across the width, or is the weakening uniform across the width? The answers to this question will help us understand the process by which a junction is made, the internal mechanisms of the junction, and help us predict how well a junction will perform in an electronic device.

Background

(i) The simplest view of how a superconductor interacts with a magnetic field is that it is completely diamagnetic: the field is deflected around the outside of the superconductor. In fact, the field is only deflected because it DOES penetrate to some extent, causing a supercurrent to flow in the penetrated regions. What we see as the repulsion of magnetic field is the result of adding the field caused by the supercurrent to that originally applied.

In our Device Physics research projects, we need to calculate the distribution of current and field inside superconducting electronic devices: Josephson junctions, SQUIDs, shielding disks etc. Because of the device geometry, and the fact that the penetration depth is often comparable to the entire size of our microfabricated devices, this must be done using numerical techniques. The problem is related to other important calculations, such as the flow of fluids, the distribution of mechanical stresses, and the deceptively simple problem of calculating inductance. Further information will be found in [1].

The project will involve calculating the field and current distribution in realistic device geometries by using existing computer algorithms, and implementing new ones. Initial results for simple situations will be compared with known solutions, and the methods will be extended to help interpret the results from our recent experiments. This project is suitable for a single student, working in collaboration with another person doing the following closely-related project.

(ii) It is difficult to observe directly the distribution of current in a Josephson junction, but it is fairly easy to measure the dependence of the junction's maximum supercurrent on an applied magnetic field. This latter measurement is sometimes called the "magnetic diffraction pattern" of the junction. Like other diffraction phenomena, the data are related to the underlying spatial distribution by a Fourier transform. In principle then, the required information can be obtained by an easily-computed inverse Fourier transform. In practice, there are some difficulties: the data contain no phase information, and experimental noise may also corrupt the data. On the other hand, we have additional information which can help: we know that the supercurrent cannot be negative, and must be zero where there is no current path, for example. Further information will be found in [2].

The aim of this project is to explore the reliability with which Fourier and Hilbert transforms can be used to compute the distribution of supercurrent within Josephson junctions, starting with simulated magnetic diffraction data, for which the correct solution will be known, and extending to real data from junctions made by the Birmingham Superconductivity group and others. It may well be possible to employ 'Monte Carlo' approaches, or the powerful 'Maximum Entropy' technique to approach this question,. The latter technique can be used to perform linear transforms on data without also transforming the noise! The work will involve the writing of computer programs to simulate the data, transform it, and compare the calculations with known results. This project is suitable for a single student, working in collaboration with another person doing the closely-related project described previously.

DESIGN & FABRICATION OF TRILAYER JOSEPHSON JUNCTIONS BY ELECTRON-BEAM
EVAPORATION & SHADOW MASK TECHNIQUE

Supervisor: Ms J Healey, Dr Mark Colclough
Room: Physics East 213, 204
Tel: 44672, 43948
e-mail: jo_healey12@hotmail.com, m.s.colclough@bham.ac.uk

Summary

To design and fabricate trilayer junctions by electron-beam evaporation and shadow mask technique. The trilayer junctions are based on superconductor-insulator-superconductor (SIS) materials, where the superconductors are niobium and the insulator is aluminium oxide. The aim of the project is to make electrical measurements on the SIS junction and probe the insulating layer by a method called anodisation spectroscopy.

Background

Quantum computing is a major ?buzz? word in the field of Condensed Matter Physics and the Birmingham Superconductivity Device Group actively participate in this field of research. Currently we are developing techniques to improve the quality and reliability of different junctions and so far we have fabricated junctions via many different techniques such as pulsed laser deposition, thermal evaporation and magnetron sputtering. However electron-beam evaporation and shadow masking [1] is a more likely candidate because;

1) Junctions can be made very small, hence have less interaction with external electromagnetic fields.

2) In-situ, to avoid any unwanted oxidisation of the superconducting layers.

3) Greater control over the thickness of each individual layer.

Therefore making and testing such devices with this process will help us to assess the likelihood for the application to quantum computing.

Many superconductivity groups throughout the world have extensily studied the electrical characteristics of SIS junctions. It has been shown that depending on the size of the insulating region determines the amount of damping on the junctions, hence different current-voltage curves and different critical currents.

The insulating layer between the two strongly superconducting electrodes provides a 'weak link' that essentially allows cooper pairs to tunnel through. However one cannot consider double particle tunnelling as the process of current flow, but rather a collective coherent wavefunction that is characterised by the number density of Cooper pairs and the phase of the Cooper pair wavefunction. The critical current of such junctions give a measure of how strongly the phases of the two superconducting electrodes are coupled through the weak link. Therefore by making electrical measurements in conjunction with anodisation spectroscopy provides a great deal of information on the insulating layer between the two superconductors.

Anodisation spectroscopy is a destructive method that relies upon slowly etching each layer away and recording how the voltage changes with time [2]. When one has etched through the superconducting layer, the following insulating layer has different current-voltage characteristics and hence changes the voltage-time response. Depending on the quality of the insulating interface with the superconductor and the thickness of the insulator provides different voltage-time curves and hence can allow one to investigate the quality of these junctions.

Therefore this project would suit a pair of students with an interest in sample preparation, electrical measurements and cryogenics to help further the research in the superconductivity device group.

[1] G. J. Dolan, 'Offset masks for lift-off photoprocessing' Applied Physics Letters 31, 337-339 (1977).
[2] T Imamura and S Hasuo, 'Characterisation of Nb/AlOx-Al/Nb junction structures by anodisation spectroscopy' IEEE Transactions on Magnetics, 25, 1131-1134 (1989).

COURSE 4 PROJECTS - YEAR 2005/6

MICROWAVE PROPERTIES OF SUPERCONDUCTORS

Supervisor: Dr Rod Ormeno (+ Philip Baker and Prof. Colin Gough)
Room: Physics East LG2
Tel:42534
e-mail: R.J.Ormeno@bham.ac.uk

Summary

In the Condensed Matter Group, we have a very successful programme to measure the electromagnetic properties of novel superconductors at microwave frequencies (typically 2-100GHz) and low temperatures. This has proved to be a valuable tool to investigate the properties of both the superconducting electrons and the thermally excited ?normal? electrons in such systems. The system we now have is far better than those used in early measurements on conventional superconductors. The proposal is for two students to extend our measurements and interpretation to conventional materials, such as lead, aluminium and niobium, to obtain new high-quality data, which will certainly tell us new things.

Background

In all superconductors, the properties of zero resistance and exclusion of small magnetic fields are due to the formation of ?Cooper pairs? of electrons. The DC resistance of a superconductor falls to zero at the critical temperature, Tc, even though not all the electrons are paired until T = 0. This is because a very small number of pairs ?shorts out? the normal unpaired electrons. When EM waves at microwave frequency are applied to a superconductor, the inertia of the electrons becomes important and electric fields are present even in a perfectly superconducting sample. Measurements at microwave frequencies of the energy dissipation in a superconductor and the exclusion of magnetic field give much extra information about the nature of the electron pairing and the properties of those electrons which are not paired.

The measurements are performed by placing a small sample of the superconductor inside a microwave resonant cavity, and observing the resultant changes in the frequency and width of the cavity resonance as a function of temperature and/or magnetic field. These are directly related to changes in the magnetic field exclusion and energy dissipation in the surface of the superconductor. Quite detailed theoretical modelling can be used to relate this to variations of the normal and superelectron densities and the change of normal electron scattering times. We have already applied these ideas to superconductors with unconventional pairing, such as High-Tc materials, where the paired electrons are in a d-state, and strontium ruthenate, which is believed to exhibit p-state pairing, with the two electrons having parallel spin. Conventional superconductors have s-state pairing of antiparallel-spin electrons, and the binding energy of Cooper pairs does not vary strongly over the Fermi surface as it does in unconventional materials.

The project would be supervised by Dr Rod Ormeno, who is in day to day charge of our internationally leading microwave facility for investigating the microwave properties of superconductors. Additional support would be provided by the rest of the microwave group in Condensed matter Physics including Prof Colin Gough (Emeritus Professor but responsible for the overall microwave programme) and Philip Baker, a current research student. The experimental programme will involve the use of either a liquid helium-3 refrigerator to reach temperatures of 0.3K, or an adiabatic demagnetisation refrigerator to extend the temperature range below 100mK.

The project will involve some sample-preparation and a balanced theoretical and experimental programme with access to world-leading experimental and computational packages for modelling. Measurements will need to be interepreted in terms of theoretical models for the microwave properties of superconductors, which will be a common area of involvement for both students.

HYBRID DEVICE STRUCTURES BASED ON CONVENTIONAL AND OXIDE (HIGH-Tc) SUPERCONDUCTORS

Supervisor: Dr Ed Tarte (Elec Eng) (+Suzanne Gildert and Drs. Chris Muirhead and Mark Colclough)
Room: Physics East E204
Tel: 44301
e-mail: E.Tarte@bham.ac.uk

Summary

The aim of this project is to fabricate hybrid Josephson junctions using oxide and conventional superconductors separated by a noble metal barrier. These devices would be based on an edge junction design which fixes the direction of current flow to be parallel to the copper-oxide planes in the oxide superconductor and enables the effect of changes in the phase of the order parameter of the superconductor to be investigated. The project will involve the design and micro-fabrication of suitable thin-film structures, as well as the necessary low-temperature measurements.

Background

The Birmingham superconductivity research group has a new program of research on superconducting quantum devices with possible applications in quantum computing. One important candidate is based upon hybrid Josephson junctions using oxide and conventional superconductors fabricated so that current flows in the copper-oxide planes of the oxide superconductor and exploits the variation of the phase of the order parameter of the oxide superconductor with crystallographic direction. In addition, hybrid junctions can be used to explore a range of novel physical phenomena associated with the order parameter of the oxide superconductor.

When a normal metal such as gold is placed in intimate contact with a conventional superconductor, since the electron wavefunctions are transmitted through the interface, the electron pairing associated with the superconductor persists for some distance into the normal metal. This proximity effect can be used to make Josephson junctions in which the supercurrent flowing through the normal metal depends on the phase difference between the superconducting order parameters on either side. However when even a metal as non-reactive as gold is deposited on the surface of a high temperature superconductor a disordered layer is formed through which electron pairs are forced to tunnel, thus decreasing the strength of the proximity effect.

Another important phenomenon which occurs at the surface of oxide superconductors is the formation of Andreev bound states. Andreev reflection is the process by which a current of single electrons in a normal metal is converted to a pair supercurrent at an interface with a superconductor. It involves the reflection of holes back along the path of the original electrons to conserve charge. For surfaces parallel to [110] directions in oxide superconductors, an electron reflected from the surface experiences a change in sign of the order parameter which induces Andreev reflection and causes the trapping of electrons at the surface. This can be observed as a peak in the conductance of the interface measured as a function of voltage.

The aim of the project proposed here is to use the superconductivity group?s existing facilities to make hybrid devices using microfabrication techniques and to investigate the Josephson effect and Andreev bound states as a function of the resistance of the gold/oxide superconductor interface and crystallographic direction. The project would only suit a pair of students with a a real commitment to and ability in hands-on experimental condensed matter physics, and excellent manual dexterity for the making of samples. We expect that the skills of the students will be such that they will also be involved in the development of electronics and software for use in low temperature tests of the junctions.

THE CLASH OF CYMBALS

Supervisor: Professor Colin Gough
Room: Physics East 203C
Tel: 44669
e-mail: C.Gough@bham.ac.uk

Summary

This project consists of two interlocking parts: a computational finite element analysis of the vibrations of parts of a musical instrument, together with measurements of the vibrational modes, and the interpretation of the results. Understanding the physics of sound production by struck instruments such as gongs and drums and relating it to the quality of sound produced by real instruments remains a largely unsolved problem. The mechanical structure and vibrational states of real instruments, which are responsible for producing the sound, are rather complicated, although simple ideas such as the existence of eigenmodes still apply. However, there are nonlinear effects at large amplitude which are important in practice. This project follows on from previous successful ones which used experimental measurements and a finite element modelling package to gain understanding of the response of a violin.

Background

The project would have three aspects:

(1)Making measurements on real and simplified instruments to measure the shapes of the modes and their frequencies.

(2)Using finite element analysis to predict the vibrational modes and modal shapes

(3)Extending both experiment and theory to the large amplitude situation.

In order to get good feedback between the experimental and theoretical aspects of this project, it is expected that both students would be involved in all aspects of the project.

The project will be within the Condensed Matter Group, where we are heavily involved in physical applications of other wave-like structures such as microwave cavities for measurements of superconducting properties. It will be supervised by Professor Gough, who is now an Emeritus Professor (retired!) but continues research on Superconductors via a major EPSRC grant, and on Musical Acoustics of violins as a Leverhulme Senior Research Fellow.

LOW TEMPERATURE MEASUREMENTS ON SUPERCONDUCTING AND MAGNETIC SAMPLES FOR LOW-ENERGY MUON STUDIES

Supervisor: Professor Ted Forgan (+Silvia Ramos & Rich Lycett)
Room: Physics East 203A
Tel: 44678
e-mail: E.M.Forgan@bham.ac.uk

Summary

Part of the research in the Condensed Matter Group, is an international collaboration with a group at the Paul Scherrer Institut in Switzerland, using a low energy muon beam to investigate the magnetic fields just inside thin films of superconductors and magnetic materials. This is world-unique research, and is producing a stream of Physical Review Letters publications. It uses the precession of the muon spin in a magnetic field as a microscopic field probe at a known depth below the surface. In preparation for our next tranche of low-energy muon beamtime in 2006, we are preparing samples of superconducting and magnetic materials, and the project would consist of measurements of resistive and magnetic properties of these samples at low temperatures. Using our highly sensitive SQUID magnetometer, for example, this would give access to the macroscopic physics of these samples. Depending on interest and beam scheduling, it may be possible for students to take part in some low energy muon beamtime. There are enough experimental projects for two students to be involved, or alternatively the second student, if they are good at theory and interested in computing, could develop the ?Maximum Entropy? technique that we are currently using to analyse the muon precession data that we obtain.

Background

The samples we are interested in include the following:

(i) Motion of magnetic flux lines in thin-film superconductors in a magnetic field: the superconductor remains ?superconducting?, but has an electrical resistance, when the flux lines are caused to move.

(ii) ?Melting? of an array of magnetic flux lines in an artificially layered High-Tc superconducting film. When magnetic field lines enter a ?Type II? superconductor, they crystallise in a (usually) hexagonal array of field lines. This ?crystal? can melt while the superconductor is still below its Tc, and the melting is more pronounced in a layered material. We would use our thin-film laser-ablation facility to produce superconducting films that are even more strongly layered than in nature in order to study this effect. The measurements in Birmingham would be mainly magnetic ones.

(iii) Proximity effect on the penetration of magnetic fields into superconductors with a layer of normal or magnetic material on their surface. This could be either with low- or high-Tc materials.

(iv) Spread of magnetism from a ferromagnetic material into a non-magnetic material: the best system for this would probably be a sandwich of iron and palladium and its temperature-dependent magnetic properties would be investigated.

This project should appeal to a pair of experimentalists with an adventurous bent and an interest in using cryogenic and thin-film techniques, or one plus a theoretician who is good at coding. Apart from Prof Forgan, a Research Fellow, Silvia Ramos and a research student, Rich Lycett are involved in this project

OBSERVATION AND INTERPRETATION OF FLUX LINE PINNING IN TYPE-II SUPERCONDUCTORS

Supervisor: Professor Ted Forgan (+Silvia Ramos & Charlotte Bowell)
Room: Physics East 203A
Tel: 44678
e-mail: E.M.Forgan@bham.ac.uk

Summary

Part of the research in the Condensed Matter Group, is the investigation of the structure and behaviour of quantised magnetic flux lines in superconductors. In a perfectly pure superconductor, such flux lines would form a two-dimensional (usually hexagonal) lattice of lines. However, this arrangement is disrupted by ?pinning? of the flux lines. The project will involve the preparation of samples with variable degrees of pinning and the measurement of their magnetisation properties using our state-of-the-art SQUID magnetometer, and the detailed interpretation of the results.

Background

We are currently using neutron diffraction experiments at International Facilities to investigate the effects of weak pinning, which is predicted to give a flux line structure called a ?Bragg Glass?; this is somewhat disordered but still gives Bragg diffraction spots. It is of interest to compare the width and shape of the tails of the Bragg peaks with independently measured degree of pinning strength. The latter will be performed by magnetisation measurements as a function of field, temperature and sample preparation. There is also expected to be a strong effect of sample shape.

The samples we are interested in include niobium with hydrogen and oxygen impurities and Pb-In alloys, which will subsequently be used for neutron diffraction experiments. We are also interested in the ?melting? of the magnetic flux lattice, which occurs in samples prepared to be very free of pinning.

This project should appeal to a pair with an interest in sample-preparation and the ability to think about magnetic properties of superconductors in the mixed state.

SUPERCONDUCTOR / FERROMAGNET INTERFACES

Supervisor: Dr Mark Colclough
Room: Physics East 204
Tel: 43948
e-mail: m.s.colclough@bham.ac.uk

Summary

This project is to make structures combining thin films of superconductors and ferromagnetic materials, and look for evidence of effects such as suppression of superconductivity caused by the transfer of electrons from the ferromagnet to the superconductor, as well as direct magnetic effects. The project may involve the design and micro-fabrication of suitable thin-film structures involving low- and high-Tc superconductors, as well as the necessary low-temperature measurements.

Background

The Birmingham superconductivity research group has a substantial ongoing programme of research on the interplay of magnetism and superconductivity. This is partly to assess candidate device technologies, but also to use phenomena at the magnet/superconductor interface as a tool to help understand the underlying physics in our chosen materials.

Theories of the effect of a ferromagnet on a superconductor involve a local alteration in superconducting order parameter, and hence in critical current and magnetic penetration depth, resulting either from the material interface or from the injection of spin-polarised electrons from the ferromagnet ("spin injection"). Additional effects arise in type II superconductors from the nucleation and subsequent motion of quantized magnetic flux lines: ?flux flow transistors? have been proposed that use this phenomenon.

The aim of the project proposed here is to extend our present work on structures in which one or more dimensions is less than one micro-metre. At this scale, the established effects become more pronounced, and we expect new quantum effects to emerge. We also wish to follow up last year?s project in this area, which produced some promising but puzzling results. In the first stage of the project, thin films of high- or low-Tc superconductor will be deposited, both on their own and with other materials. These will have their low temperature properties measured, to be sure of the quality of the starting materials. After making suitable contacts, and possibly micro-patterning, complementary measurements can be made of the transport and magnetic properties.

The project would suit a pair of students with an interest in hands-on experimental condensed matter physics, and good manual dexterity for the making of samples.

COMPUTATIONS FOR SUPERCONDUCTORS AND MAGNETIC FIELDS

Supervisor: Dr Mark Colclough
Room: Physics East 204
Tel: 43948
e-mail: m.s.colclough@bham.ac.uk

Summary

This is a pair of closely-related computational superconductivity projects:

Background

The aim of this project is to explore the reliability with which Fourier and Hilbert transforms can be used to compute the distribution of supercurrent within Josephson junctions, starting with simulated magnetic diffraction data, for which the correct solution will be known, and extending to real data from junctions made by the Birmingham Superconductivity group and others. It may well be possible to employ the powerful ?Maximum Entropy? technique to approach this question. This technique can be used to perform linear transforms on data without also transforming the noise! The work will involve the writing of computer programs to simulate the data, transform it, and compare the calculations with known results. This project is suitable for a single student, working in collaboration with another person doing the closely-related project described previously.

COURSE 4 PROJECTS - YEAR 2012/13

HAS ROOM TEMPERATURE SUPERCONDUCTIVITY BEEN OBSERVED IN WATER-TREATED GRAPHITE POWDER?

Summary and Perspectives (by PD and MR)

COURSE 4 PROJECTS - YEAR 2011/12

QUANTUM FLUCTUATIONS IN SUPERCONDUCTING NIOBIUM

Summary and Perspectives

COURSE 4 PROJECTS - YEAR 2010/11

X-RAY STUDY OF THIN FILMS OF INDIUM TIN OXIDE, A TRANSPARENT CONDUCTOR

Summary and Perspectives (by DF)

COURSE 4 PROJECTS - YEAR 2009/10

POLYSTYRENE AND POLYANILINE THIN FILMS

Summary and Perspectives (by AF and CO'N)

COURSE 4 PROJECTS - YEAR 2007/8

ULTRA-HIGH PURITY SUPERCONDUCTORS AT LIQUID He TEMPERATURES

Summary

Background

Further Reading

COMPUTATIONS FOR SUPERCONDUCTORS AND MAGNETIC FIELDS

Summary

Background

Further Reading

DESIGN & FABRICATION OF TRILAYER JOSEPHSON JUNCTIONS BY ELECTRON-BEAM EVAPORATION & SHADOW MASK TECHNIQUE

Summary

Background

COURSE 4 PROJECTS - YEAR 2005/6

MICROWAVE PROPERTIES OF SUPERCONDUCTORS

Summary

Background

HYBRID DEVICE STRUCTURES BASED ON CONVENTIONAL AND OXIDE (HIGH-Tc) SUPERCONDUCTORS

Summary

Background

THE CLASH OF CYMBALS

Summary

Background

LOW TEMPERATURE MEASUREMENTS ON SUPERCONDUCTING AND MAGNETIC SAMPLES FOR LOW-ENERGY MUON STUDIES

Summary

Background

OBSERVATION AND INTERPRETATION OF FLUX LINE PINNING IN TYPE-II SUPERCONDUCTORS

Summary

Background

SUPERCONDUCTOR / FERROMAGNET INTERFACES

Summary

Background

COMPUTATIONS FOR SUPERCONDUCTORS AND MAGNETIC FIELDS

Summary

Background

DESIGN & FABRICATION OF TRILAYER JOSEPHSON JUNCTIONS BY ELECTRON-BEAM
EVAPORATION & SHADOW MASK TECHNIQUE